I. Field
The present disclosure relates generally to electronics circuits, and more specifically to an amplifier.
II. Background
Amplifiers are commonly used in various applications such as communication, audio, etc. Amplifiers may be categorized into different classes such as class A, class B, class AB, and class D. Class A, B and AB amplifiers are linear amplifiers that operate in linear region. Class D amplifiers are switching amplifiers that operate in triode and cut-off regions. Consequently, class D amplifiers can typically achieve much higher power efficiency than linear amplifiers.
A class D amplifier is commonly used with a modulation technique such as pulse width modulation (PWM) or pulse density modulation (PDM). A PWM modulator typically receives an analog input signal and a carrier signal and generates a PWM drive signal that controls the switching of the class D amplifier. The PWM drive signal has (i) a variable duty cycle that is determined by the amplitude of the analog input signal and (ii) a fixed switching frequency that is determined by the frequency of the carrier signal. The carrier signal may have a sawtooth waveform or a triangular waveform. An output signal from the class D amplifier typically includes strong harmonics of the carrier signal. An output filter is typically coupled to the output of the class D amplifier and used to attenuate the harmonics of the carrier signal. However, the output filter typically occupies a large circuit area in order to provide sufficient attenuation of the carrier signal harmonics.